Using the Powersim™ software platform, a dynamic systems model was built to explore the
surface water supply in the Middle Rio Grande in New Mexico from Cochiti Dam to Elephant
Butte Dam. A number of similar models exist but do not include a spatial component and/or
attempt to model terms with a great deal of uncertainty, such as riparian evapotranspiration,
ungaged tributary inflow, and effective precipitation. This model simulates the Middle Rio
Grande in six reaches, extending from Cochiti Dam to Elephant Butte Dam, a distance of
approximately 175 miles. Ungaged tributary inflow and effective precipitation are successfully
included through the use of an ArcGIS-based hydrologic analysis and precipitation profiles built
with paleoprecipitation reconstructions for New Mexico over the last 1000 years. The simulation
results are compared to gaged river flows over the past 50 years through a probabilistic
distribution analysis. Generally, probabilistic analysis indicates the model may be optimistic in its
estimation of river flows, although not in the year to year variability of those flows. Thus, either
the inflows are overestimated by the model relative to the last 50 years, or the outflows are
underestimated, or a combination of both. However, comparison of the distribution of the
precipitation profile data source (1000 years long) and the model precipitation profiles indicate
inflows are appropriately simulated. Alternatively, the model seems to represents the last 50
years fairly well in the upper reaches, but has difficulty in the lower reaches. Nevertheless, the
model can provide useful information when comparing simulation results to each other. Year to
year variability is very high and clearly maintained from gage to gage. Not surprisingly, the very
dry climate is the “worst” climate scenario, with a lowest average flow at San Marcial of 691 cfs.
The “best” scenario was the moderately wet and consistent climate with an average flow of 1053
cfs at San Marcial. When considering compliance with the Rio Grande Compact, the average
consistent climate was the worst, generating 38 years of accrued debit status and 18 years of
annual debits. A correlation analysis indicated gage flows for each reach have a positive 1 to 1
correlation with sub-basin runoff. Open water evaporation was positively correlated to a
moderate extent with gage flows, reflecting the influence of surface area on evaporation. In
addition to these analyses, the simulation results revealed the effects of the price of water by
using an economic demand equation. A “conservation” price path was designed to meet
Albuquerque’s goals of 150 gpcd by 2014 and 130 gpcd by 2040. This path and a 2.5 percent
annual increase price path caused immediate reductions in the total demand volume and
reductions in the San Juan-Chama diversion by 2014. However, the conservation price path led
to a rebound in the diversion, with full diversion again occurring by 2038 even though per capita
use was only 132 gpcd. The 2.5 percent price path began to rebound in 2032 when per capita
use reached the imposed lower limit of 75 gpcd. More moderate price increases of 1.25 percent
and 1.5 percent reduced the San Juan-Chama diversion in 2042 and 2030, respectively. No
rebound occurred and per capita use reached a low of 75 gpcd and 101 gpcd by 2053. The 1.5
percent or 2.5 percent annual price increases converged in 2053 at a maximum reduction of the
San Juan-Chama diversion at almost 62,000 AF per year, with per capita use of 75 gpcd. While
reduction of the San Juan-Chama diversion led to increases in the flow at the Albuquerque gage,
declines in per capita use resulted in decreases at the Bernardo gage, caused by declines in
wastewater return flows in that reach. The simulated drop in the Bernardo gage flow was small,
less than an annual average of 45 cfs at its maximum. Although the model produced simulation
results with a “wetter” distribution than the past 50 years, it provides a platform for exploring the
relative impact of management alternatives. Interestingly, the averages are not as far apart as
the probabilistic distribution. Thus, “average” is a dangerous word for the Middle Rio Grande
and may misrepresent future climates and river flows.

This publication is the Professional Project report of Ann D. Demint, submitted in partial
fulfillment of the requirements for the Master of Water Resources degree at the University of
New Mexico (December 2005).